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I don't even see anything like that on my Galaxy s21, so I think you are talking about an old Samsung feature that no longer exists (the only setting I have for it is to toggle whether it puts 4 "suggestions" icons based on recent usage at the bottom of the screen). What you see now is the standard Android recents screen of the last few years - prior to that the norm was a set of icons and names but no live images.
Apps that are really sensitive can blank themselves out on the recents screen, e.g. my banking or encrypted notes apps do this. So maybe you could check the settings of say your email app to see whether there is an option, or contact the developer?
I'll be honest, I do find it useful being able to check a piece of information on a recent app without having to switch to it, and use that surprisingly often. I don't regard it as a huge security risk, as it only shows one app at a time so I could swipe past an email before anyone can read it - using a phone in public without awareness of who might be looking over your shoulder is a security risk per se, and I don't think this feature changes that either way really. I can see a greater potential for embarrassment, but after using it for several years I've overall found it a benefit.